The major goal of the proposed work is to purify and characterize proteins of the mouse eukaryotic cell plasma membrane. Previously, a library of monoclonal antibodies that specifically precipitate many mouse cell surface proteins have been prepared. These antibodies are now being used for characterization of some of the proteins that are initially of greatest interest. One of the major components of the cell surface is a glycoprotein of about 80,000 daltons, with about 10 to the 6th power copies per cell. This glycoprotein has been found to be a allospecific differentiation antigen of mesenchymal cells. Current studies are: (1) the analysis of this protein of macrophages, (2) the genetic mapping of the protein, (3) the topography of the protein in the cell plasma membrane, and (4) protein purification. A second protein of major interest is a 90,000 dalton major cell surface glycoprotein also present in about 10 to the 6th power copies per cell. Current studies involve the apparent relationship of this protein to the cell plasma membrane and the coprecipitation by monoclonal antibodies of a protein of 70,000 daltons that has been identified as a major heat-shock inducable constituent of murine fibroblasts. A third study concerns a cell surface protein of about 150,000 daltons. Immunoprecipitates of the protein with monoclonal antibodies catalyzed the incorporation of P32 ATP into phosphate acceptor proteins. This membrane protein kinase is now being characterized. Studies in progress with each of these proteins include the characterization of the monoclonal antibodies, analysis of the physical and biological properties of the antigen, and purification of the proteins.